You would be best off seeking the advice of a diesel specialist to be honest, but if it were me i would be probably gamble and see if there is a regulator available as a separate component for the pump.(the high pressure pump)

The esp light might be unrelated, i cant see why the 2 would be related?

pity your not closer i have a 2.0 ltr off the road which you could of borrowed the parts off to see if it was either or i do have a spare fuel rail with the reg on i might be able to loan you pm me if you want

pity your not closer i have a 2.0 ltr off the road which you could of borrowed the parts off to see if it was either or i do have a spare fuel rail with the reg on i might be able to loan you pm me if you want